Voltage converter with buck converter and low dropout regulator

ABSTRACT

A voltage converter includes a low dropout regulator voltage converter circuit. The voltage converter generates three voltages (e.g., 1.2 volts, 2.5 volts, and 1.8 volts) for an electronic system, which can be a smartphone or electronic tablet or other device. An implementation has at least one charge pump voltage converter circuit. The low dropout regulator voltage converter circuit provides an output voltage based on its input voltages and can operate with a very small input-to-output differential voltage. Compared to using a Buck converter, a low dropout regulator does not have an external inductor, which saves space. An implementation of the voltage converter can also include at least one charge pump voltage converter circuit to generate a voltage of the voltage converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser. No. 14/455,753, filed Aug. 8, 2014, which claims the benefit of U.S. patent application 61/863,820, filed Aug. 8, 2013. These applications are incorporated by reference along with all other references cited in this application.

BACKGROUND OF THE INVENTION

The invention is related to the field of electrical circuits and more specifically to voltage converter circuits for electronic circuitry.

Electronic circuitry is used wide range of applications, systems, and devices including computer monitors, televisions, instrument panels, aircraft cockpit displays, signage, laptop computers, video players, music players, gaming devices, clocks, watches, calculators, telephones, smartphones, tablets, and many other devices.

These devices can include transistors, logic gates, memory, display panels, and other circuits and technologies. The electronics are used in a system typically operate at different voltage levels from each other. But external voltage is supplied from a direct current (DC) supply or a battery source is at a single voltage level.

Therefore, there is a need for circuitry to perform DC-to-DC voltage conversion to generate voltages at different voltages levels that allow the electronic system of the system to operate properly. And it is desirable that the voltage conversion is performed with higher efficiency to reduce power consumption.

BRIEF SUMMARY OF THE INVENTION

A voltage converter includes a low dropout regulator voltage converter circuit. The voltage converter generates three voltages (e.g., 1.2 volts, 2.5 volts, and 1.8 volts) for an electronic system, which can be a smartphone or electronic tablet or other device. An implementation has at least one charge pump voltage converter circuit. The low dropout regulator voltage converter circuit provides an output voltage based on its input voltages and can operate with a very small input-to-output differential voltage. Compared to using a Buck converter, a low dropout regulator does not have an external inductor, which saves space. An implementation of the voltage converter can also include at least one charge pump voltage converter circuit to generate a voltage of the voltage converter.

Specifically, a voltage converter can include at least one charge pump voltage converter circuit. The charge pump voltage converter circuit provides an output voltage that is an average of its input voltages. Compared to a low dropout regulator, a charge pump voltage converter circuit has higher efficiency. This voltage converter will save power compared to converters using a low dropout regulator. An implementation of the voltage converter can includes at least two charge pump voltage converter circuits to generate to different output voltages.

Circuitry that performs voltage conversion with higher efficiency will reduce power consumption. This helps increase the run time of battery operated devices. In a specific implementation, the circuitry includes a floating charge pump circuit including two different input voltages. For example, neither of the two voltage inputs is connected to ground in a specific implementation. The output voltage of the floating charge pump circuit is an average of the two voltage inputs.

In an implementation, a circuit includes: an input voltage; a first buck circuit, connected to the input voltage, generating a first output voltage; a second buck circuit, connected to the first input voltage, generating a second output voltage, where the second output voltage is higher than the first output voltage; and a low dropout regulator circuit, connected to the second output voltage, generating a third output voltage, where the third output voltage is between the first and second output voltages.

In an implementation, a circuit includes: an input voltage; a first buck circuit, connected to the input voltage, generating a first output voltage; a second buck circuit, connected to the first input voltage, generating a second output voltage, where the second output voltage is higher than the first output voltage; and a charge pump circuit, connected to the first and second output voltages, generating a third output voltage, where the third output voltage is between the first and second output voltages.

In an implementation, a circuit includes: an input voltage; a buck circuit, connected to the input voltage, generating a first output voltage; a first charge pump circuit, connected to the first input voltage, generating a second output voltage, where the second output voltage is lower than the first output voltage; and a second charge pump circuit, connected to the first and second output voltages, generating a third output voltage, where the third output voltage is between the first and second output voltages.

In various implementations, the charge pump circuit includes: a first switch, connected between the first output voltage and a first node; a second switch, connected between the first node and the third output voltage; a third switch, connected between the third output voltage and a second node; a fourth switch, connected between the second node and the second output voltage; and a charge pump capacitor, connected between the first and second nodes.

The first and third switches are connected to a first signal line, and the second and fourth switches are connected to a second signal line. A signal on the first signal line is out of phase with a signal on the second signal line.

The first node is connected to a positive plate of the charge pump capacitor, and the second node is connected to a negative plate of the charge pump capacitor.

The first charge pump includes: a first switch, connected between the first output voltage and a first node; a second switch, connected between the first node and the second output voltage; a third switch, connected between the second output voltage and a second node; a fourth switch, connected between the second node and a ground voltage; and a first charge pump capacitor, connected between the first and second nodes.

The second charge pump includes: a fifth switch, connected between the first output voltage and a third node; a sixth switch, connected between the third node and the third output voltage; a seventh switch, connected between the third output voltage and a fourth node; an eighth switch, connected between the fourth node and the second output voltage; and a second charge pump capacitor, connected between the third and fourth nodes.

The first and third switches are connected to a first signal line, and the second and fourth switches are connected to a second signal line. A signal on the first signal line is out of phase with a signal on the second signal line.

The first and third switches are connected to a first signal line, the second and fourth switches are connected to a second signal line, the fifth and seventh are connected to a third signal line, and the sixth and eight switches are connected to a fourth signal line.

A first signal on the first signal line is out of phase with a second signal on the second signal line, and third signal on the third signal line is out of phase with a fourth signal on the fourth signal line. Alternatively, a first signal on the first signal line is out of phase with a second signal on the second signal line, the first signal is on the third signal line, and the second signal is on the fourth signal line.

The first node is connected to a positive plate of the first charge pump capacitor, and the second node is connected to a negative plate of the first charge pump capacitor. The first node is connected to a positive plate of the first charge pump capacitor, the second node is connected to a negative plate of the first charge pump capacitor, the third node is connected to a positive plate of the second charge pump capacitor, and the fourth node is connected to a negative plate of the second charge pump capacitor.

Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an electronic system.

FIG. 2 shows an implementation of a voltage generator to generate three different voltages using buck converters.

FIG. 3 shows a charge pump voltage converter.

FIGS. 4A and 4B show a further implementation of a charge pump voltage converter.

FIG. 5 shows an implementation of a voltage generator using at least one charge pump voltage converter.

FIG. 6 shows an implementation of a voltage generator using at least two charge pump voltage converters.

FIG. 7 shows a charge pump circuit.

FIGS. 8A and 8B show phases of operation of the charge pump circuit.

FIG. 9 shows a power management integrated circuit.

FIG. 10 shows the power management integrated circuit in a single charge pump application.

FIG. 11 shows two power management integrated circuits in a two charge pump application.

FIG. 12 shows a low dropout regulator circuitry.

FIG. 13 shows a connectivity between a buck circuit of an integrated circuit and an external inductor.

FIG. 14 shows a connectivity between of buck circuits of an integrated circuit to two external inductors.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram an electronic system or electronic device 101. The electronic system includes electronic circuitry 103, a voltage converter 106, a multiplexer 109, and a battery source 112.

In a specific implementation, the system is a smartphone or tablet computer, but can include device types such as computer monitors, televisions, instrument panels, aircraft cockpit displays, signage, laptop computers, video players, music players (e.g., Apple's iPod product family), gaming devices, cameras, clocks, watches, calculators, telephones, smartphones (e.g., Apple's iPhone product family, Google's Nexus product family, Samsung's Galaxy product family), tablets (e.g., Apple's iPad product family, Google's Nexus product family, or Samsung's Galaxy product family), and many others.

The electronic circuitry includes, among other components, transistors (e.g., bipolar, MOS, or others), logic gates (e.g., NAND, NOR, AND, OR, XOR, or others), memory (e.g., RAM, flash, or others), display (e.g., flat panel, liquid crystal display (LCD), organic light emitting diode (OLED), or others), and combinations of these. The electronic circuitry and components can include central processing units (CPUs), analog-to-digital converters (ADCs), digital-to-analog converters (DACs), amplifiers and operational amplifiers (e.g., op amp), and many others.

To operate, power is supplied to the electronic circuitry at one or more voltage levels. For example, the electronic circuitry can use three voltages, VOUT1, VOUT2, and VOUT3, at three different voltage levels. These voltages are generated by voltage generator 106. In a specific implementation, such as for a tablet device, the voltages are 1.2 volts, 2.5 volts, and 1.8 volts. These voltages can be used for the logic supplies for the timing controlling and source driver integrated circuit (IC). The 2.5-volt supply is capable of supplying up to about 50 milliamps. The 1.8-volt supply is capable of supplying up to about 50 milliamps. And in another implementation, the 1.8-volt supply is capable of supplying up to about 200 to about 300 milliamps.

Voltage converter 106 generates output voltages VOUT1, VOUT2, and VOUT3 from an input voltage VIN. VIN can be from a DC supply (e.g., VDD or VCC) or battery 112, in case of a portable device or device with battery source (such as for battery back-up). In system 101, VDD or battery 112 is passed through multiplexer 109 to VIN of the voltage converter. For a system without a battery source, VDD is directly connected to VIN, and the battery and multiplexer can be omitted.

Typically VDD is a regulated DC source at about 3.3 volts. The DC source can vary and range plus or minus about 10 percent (e.g., ranging from about 2.97 volts to about 3.63 volts). These variations can of because of fluctuations in an AC supply to the DC source, temperature changes, variations in components (e.g., size variation of capacitors, resistors, and inductors), and other factors.

The battery source can be made from various battery chemistry technologies, such as lithium ion, lithium polymer, lithium air, nickel metal hydride, nickel cadmium, and others. Depending on the chemistry, the voltage output from the battery cell can vary. For a single lithium ion cell, the output voltage is typically about 3.7 volts, but can vary from a minimum of about 3.2 volts (or 2.9 volts in some cases) to a maximum of about 4.2 volts. Further, depending on an amount of charge stored in the battery, the output voltage will vary over time until the battery is discharged or depleted.

The voltage converter is a DC-to-DC converter that takes the VIN voltage and generates the output voltages for the electronic circuitry of the system. FIG. 2 shows an implementation of a voltage converter where VOUT1 (1.2 volts) is generated by a buck converter from VIN, VOUT2 (2.5 volts) is generated by a buck converter from VIN, and VOUT3 (1.8 volts) is generated by a low dropout regulator (LDO) from VOUT2.

A buck converter is a step-down DC-to-DC converter that uses inductors. Buck converters have a theoretical efficiency of 100 percent. But in actual use, the buck converter for VOUT1 (1.2 volts) has an efficiency of about 85 percent and VOUT2 (2.5 volts) of about 92 percent. The inductor of a Buck converter is an external or off-chip inductor, which is generally costly and requires some space on a printed circuit board.

A low dropout regulator is a linear voltage regulator which can operate with a very small input-to-output differential voltage. The main components are a power FET and a differential amplifier (error amplifier). One input of the differential amplifier monitors the fraction of the output determined by the resistor ratio of R1 and R2. The second input to the differential amplifier is from a stable voltage reference (bandgap reference). If the output voltage rises too high relative to the reference voltage, the drive to the power FET changes to maintain a constant output voltage.

An efficiency of the low dropout regulator for VOUT3 is fixed by the ratio of VOUT3/VIN3, where VIN3 is the VIN to the low dropout regulator. Therefore, an efficiency for generating VOUT3 is about 1.8/2.5 which is about 72 percent. This is much less than the theoretical efficiency of 100 percent of the buck converters. Therefore, improving the power efficiency for the generation of VOUT3 (1.8 volt) will improve the overall efficiency of the system. And this will improve battery run time of the device.

Another technique for performing DC conversion is to use a charge pump (CP). A charge pump is a DC-to-DC converter that uses capacitors as energy storage elements to create either a higher or lower voltage power source. The efficiency of a charge pump is typically 90 to 90 percent, which is better than for a low dropout regulator.

FIG. 3 shows a charge pump connected to an input voltage VIN and ground, and generating an output voltage VO. The output voltage of this charge pump will be (VIN plus ground)/2 or VIN/2. Specifically, the output voltage VO for the charge pump is ½ of the input voltage VIN.

FIG. 4A shows a charge pump configuration having inputs VIN1 and VIN2. In the FIG. 3 configuration, VIN2 is connected to ground. But in this configuration, VIN2 is connected to another voltage value. The output voltage of this charge pump will be (VIN plus VIN2)/2 or VIN/2. Specifically, the output voltage VO for the charge pump is an average of input voltages VIN1 and VIN2.

FIG. 4B shows the charge pump configuration of FIG. 4A with connections to VCC and ground. The charge pump configuration in FIGS. 4A and 4B can be referred to as a floating charge pump (FCP). In a specific implementation, the charge pump is unregulated, but in other implementations, the charge pump is regulated. Compared to a buck converter, by eliminating the inductor, these switched capacitor converters provided small solution footprint and a simpler design.

FIG. 5 shows an implementation of voltage converter with two buck converters and a charge pump converter. Specifically, compared to the FIG. 2 configuration, instead of using a low dropout regulator for VOUT3 (1.8 volts), a floating charge pump is used instead. VIN1 and VIN2 of the floating charge pump are connected to VOUT1 (1.2 volts) and VOUT2 (2.5 volts). Then, voltage output VO of the floating charge pump (which is VOUT3) will be 1.8 volts (i.e., (1.2+2.5)/2).

FIG. 6 shows another implementation of voltage converter with one buck converter and two charge pump converters. Specifically, voltage VOUT2 (2.5 volts) is generated using a buck converter. Voltages VOUT1 (1.2 volts) and VOUT3 (1.8 volts) are generated by way of floating charge pumps.

Voltage VOUT2 (2.5 volts) is used as an input by a charge pump to generate an output voltage VOUT1 (1.25 volts). In this implementation, VOUT1 is not exactly at 1.2 volts, but rather 1.25 volts, but this is still in within a 10 percent margin range of 1.2 volts that the electronic circuitry will work properly.

Voltage VOUT3 (1.8 volts) is generated by VOUT1 (1.25 volts) and VOUT2 (2.5 volts), which is more specifically 1.875 volts. Even though 1.875 volts is not exactly at 1.8 volts, this is still in within a 10 percent margin range of 1.8 volts that the electronic circuitry will work properly.

Compared to the FIG. 2 voltage converter configuration, by using one buck converter and a low dropout regulator, this reduces the number of external or off-chip inductors needed, and also increases an energy efficiency of the device. This will improve the battery run time of the device.

FIG. 7 shows a specific implementation of charge pump. The charge pump has a capacitor Cf connected to four switches. A first switch connects a positive plate of the capacitor to VIN1. A second switch connects a positive plate of the capacitor to VOUT. A third switch connects a negative plate of the capacitor to VOUT. And a fourth switch connects a negative plate of the capacitor to VIN2.

Also there are capacitors between VIN1 and ground, VOUT and ground, and VIN2 and ground. There can be external capacitors, internal capacitors, or parasitic capacitances, and are used to stabilize the voltages at those nodes.

In operation, the switches are connected to a clock signal. The clock signal has a 50 percent duty cycle. Pairs of switches operate out of phase with each other. Specifically, the first and third switches are closed during a first phase and opened during a second phase. The second and fourth are open during the first phase and closed during the second phase.

In a specific implementation, VIN1 is 2.5 volts and VIN2 is 1.2 volts. Then VOUT will be 1.85 volts where there is a 0.65 volt different across the capacitor.

FIG. 8A shows a circuit diagram of the FIG. 7 circuit during the first phase. FIG. 8B shows a circuit diagram of the FIG. 7 circuit during the second phase.

This technique of using a charge pump to obtain an output voltage that is an average its two input voltages can be used in a variety of applications, such as voltage converter as described above, integrated in a power management integrated circuit (PMIC), standalone, discrete component use, integrated circuit use, and many others.

As an example, FIG. 9 shows a power management integrated circuit. The integrated circuit has ten external pins: Pin 1 is ground. Pin 2 is VDD, integrated circuit supply. Pin 3 is CLKB, inverted clock output. Pin 4 is CK, clock input, 50 percent duty cycle clock. Pin 5 is EN, enable pin; set EN to high to enable output. Pin 6 is OUT, charge pump output. Pin 7 is CP1, first pin for fly capacitor. Pin 8 is for CP2, second pin for fly capacitor. Pin 9 is NP, which is connected to ground for 1.2-volt output or connected to 1.2-volt supply for 1.8-volt output. Pin 10 is VIN, supply for charge pump.

The VIN and CP1 pins are connected to first node of a first capacitor (e.g., transistor connected as a capacitor), while a second node of the capacitor is connected to pulse width modulation (PWM) logic and drive block. The CP1 and VOUT pins are connected to first node of a second capacitor, while its second node is connected to the PWM block. The VOUT and CP2 pins are connected to first node of a third capacitor, while its second node is connected to the PWM block. The CP2 and NP pins are connected to first node of a fourth capacitor, while its second node is connected to the PWM block.

FIG. 10 shows the power management integrated circuit configured in a single charge pump application. There is a VOUT voltage of 1.2 volts.

FIG. 11 shows two power management integrated circuits configured in a two charge pump application. There are two VOUT voltages of 1.2 volts and 1.8 volts.

FIG. 12 shows a low dropout regulator circuitry. The circuitry includes a power transistor. A differential amplifier has a first input, a second input, and an output connected to an input of the power transistor. The first input of the differential amplifier is connected to monitor a fraction of an output determined by a ratio of resistor R1 and resistor R2. The first input is connected to a reference voltage. The low dropout regulator circuitry is not configured to be connected to an external or off-chip inductor.

FIG. 13 shows a connectivity between a buck circuit of an integrated circuit and an external inductor. The buck circuit is connected via an external connection of the integrated circuit to the external or off-chip inductor.

FIG. 14 shows a connectivity between of buck circuits of an integrated circuit to two external inductors. A first buck circuit is connected via a first external connection of an integrated circuit to a first external or off-chip inductor. A second buck circuit is connected via a second external connection of the integrated circuit to a second external or off-chip inductor.

This description of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. For example, some specific voltage levels are described, but other voltage levels can be used and generated instead. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications. This description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications as are suited to a particular use. The scope of the invention is defined by the following claims. 

The invention claimed is:
 1. A circuit comprising: an input voltage; a first buck circuit, coupled to the input voltage, generating a first output voltage; a second buck circuit, coupled to the input voltage, generating a second output voltage, wherein the second output voltage is higher than the first output voltage; and a low dropout regulator circuit, coupled to the second output voltage, generating a third output voltage, wherein the third output voltage is between the first and second output voltages, wherein the third output voltage is between the first and second output voltages, and the low dropout regulator circuit comprises a power transistor, and a differential amplifier comprising a first input, a second input, and an output, wherein the first input monitors a fraction of the output determined by a resistor ratio of a first resistor and a second resistor, the second input is coupled to a reference voltage, and the output is coupled to the power transistor, an operating efficiency of the low dropout regulator circuit is less than the first buck circuit and less than the second buck circuit, and the operating efficiency of the low dropout regulator circuit is related to the third output voltage divided by the second output voltage, wherein the first output voltage is about 1.2 volts, the second output voltage is about 2.5 volts, and the third output voltage is about 1.8 volts.
 2. The circuit of claim 1 wherein the reference voltage is generated by a bandgap reference.
 3. The circuit of claim 1 wherein the first buck circuit is coupled to a first off-chip inductor.
 4. The circuit of claim 3 wherein the second buck circuit is coupled to a second off-chip inductor.
 5. The circuit of claim 1 wherein the third output voltage is capable of supplying more current than a current supplying capability of the second output voltage.
 6. The circuit of claim 1 wherein the third output voltage is capable of supplying about 50 milliamps or more, which is greater than a current supplying capability of the second output voltage.
 7. An integrated circuit comprising: an input voltage; a first buck circuit, coupled to the input voltage, generating a first output voltage, wherein the first buck circuit is configured to be coupled to a first off-chip inductor; a second buck circuit, coupled to the input voltage, generating a second output voltage, wherein the second output voltage is higher than the first output voltage, and the second buck circuit is configured to be coupled to a second off-chip inductor; and a low dropout regulator circuit, coupled to the second output voltage, generating a third output voltage, wherein the third output voltage is between the first and second output voltages, and the low dropout regulator circuit comprises a power transistor, and a differential amplifier comprising a first input, a second input, and an output, wherein the first input is coupled to monitor a fraction of the output determined by a resistor ratio of a first resistor and a second resistor, the second input is coupled to a reference voltage, and the output is coupled to the power transistor, and an operating efficiency of the low dropout regulator circuit is less than the first buck circuit and less than the second buck circuit, wherein the first output voltage is about 1.2 volts, the second output voltage is about 2.5 volts, and the third output voltage is about 1.8 volts.
 8. The integrated circuit of claim 7 wherein the operating efficiency of the low dropout regulator circuit is about the third output voltage divided by the second output voltage.
 9. The integrated circuit of claim 7 wherein the third output voltage is capable of supplying about 200 milliamps or more, which is greater than a current supplying capability of the second output voltage.
 10. The integrated circuit of claim 9 wherein the second output voltage is capable of supplying up to about 50 milliamps.
 11. The integrated circuit of claim 7 wherein the third output voltage is capable of supplying up to about 50 milliamps.
 12. A device comprising: an integrated circuit comprising: an input voltage; a first buck circuit, coupled to the input voltage, generating a first output voltage; a second buck circuit, coupled to the input voltage, generating a second output voltage, wherein the second output voltage is higher than the first output voltage; and a low dropout regulator circuit, coupled to the second output voltage, generating a third output voltage, wherein the third output voltage is between the first and second output voltages, and the low dropout regulator circuit comprises a power transistor, and a differential amplifier comprising a first input, a second input, and an output, wherein the first input monitors a fraction of the output determined by a resistor ratio of a first resistor and a second resistor, the second input is coupled to a reference voltage, and the output is coupled to the power transistor, an operating efficiency of the low dropout regulator circuit is less than the first buck circuit and less than the second buck circuit, and the operating efficiency of the low dropout regulator circuit is related to the third output voltage divided by the second output voltage, the first output voltage is about 1.2 volts, the second output voltage is about 2.5 volts, and the third output voltage is about 1.8 volts, the third output voltage is capable of supplying about 200 milliamps or more, which is greater than a current supplying capability at the second output voltage.
 13. The device of claim 12 comprising: a first inductor, not formed on the integrated circuit, wherein the first buck circuit is coupled via an external connection of the integrated circuit to the first inductor.
 14. The device of claim 13 comprising: a second inductor, not formed on the integrated circuit, wherein the second buck circuit is coupled via an external connection of the integrated circuit to the second inductor.
 15. The circuit of claim 1 wherein the first buck circuit is formed on an integrated circuit, and a first inductor, not formed on the integrated circuit, and the first buck circuit is coupled via an external connection of the integrated circuit to the first inductor.
 16. The device of claim 15 wherein the second buck circuit is formed on an integrated circuit, and a second inductor, not formed on the integrated circuit, and the second buck circuit is coupled via an external connection of the integrated circuit to the second inductor.
 17. The integrated circuit of claim 7 comprising: a first inductor, not formed on the integrated circuit, wherein the first buck circuit is coupled via an external connection of the integrated circuit to the first inductor.
 18. The integrated circuit of claim 17 comprising: a second inductor, not formed on the integrated circuit, wherein the second buck circuit is coupled via an external connection of the integrated circuit to the second inductor. 